Part of the work performed during the development of this invention utilized U.S. government funds under grants No. CHE92-96013 and No. CHE93-20611 from the National Science Foundation, Chemistry Division, Analytical and Surface Science. The government may have certain rights in this invention.
1. Field of the Invention
This invention relates generally to a method for forming and exploiting gradients at the interfaces between components of a composite material as well as the composite material itself and devices which incorporate the material. In particular, the invention relates to a method for forming and exploiting magnetic gradients at the interfaces between components of a composite magnetic material and the magnetic composite material itself as well as devices which incorporate the composite material such as electrochemical systems and separators including fuel cells, batteries, membrane sensors, flux switches, chromatographic separations, and nonelectrochemical separations resulting in enhanced and modified flux and performance in those systems. The invention also relates to apparatus, methods of making, and methods of using composite magnetic materials and interface gradients for the separation of transition metals, both light and heavy, from other species and from each other.
2. Background of the Related Art
In the detailed description of preferred embodiments, it will be shown that interfacial gradients in properly prepared composite materials can be exploited to enhance flux in many types of electrochemical systems such as fuel cells, batteries, membrane sensors, filters and flux switches. Such interfacial gradients may also be exploited in separators involving chromatographic separations and nonelectrochemical separations including, but not limited to, separations of light and heavy transition metals and transition metal complexes. The heavy transition metals include the lanthanides and the actinides which have atomic numbers 58-71 and 90-103, respectively. First, however, the following discussion provides a brief overview of the current understanding of magnetic properties in composites. In particular, the discussion below summarizes the thermodynamic, kinetic and mass transport properties of bulk magnetic materials. These bulk properties of molecules in magnetic fields are fairly well understood.
Paramagnetic molecules have unpaired electrons and are attracted into a magnetic field; diamagnetic species, with all electrons paired, are slightly repelled by the field. Radicals and oxygen are paramagnetic; most organic molecules are diamagnetic; and most metal ions and transition metal complexes are either para- or diamagnetic. How strongly a molecule or species in a solution or fluid responds to a magnetic field is parameterized by the molar magnetic susceptibility, Xm (cm3/mole). For diamagnetic species, Xm is between (xe2x88x921 to xe2x88x92500)xc3x9710xe2x88x926 cm3/mole, and temperature independent. For paramagnetic species, Xm ranges from 0 to +0.01 cm3/mole, and, once corrected for its usually small diamagnetic component, varies inversely with temperature (Curie""s Law).
While ions are monopoles and will either move with or against an electric field, depending on the sign of the ion, paramagnetic species are dipoles and will always be drawn into (aligned in) a magnetic field, independent of the direction of the magnetic vector. These dipoles will experience a net magnetic force if a field gradient exists. Because electrochemistry tends to involve single electron transfer events, the majority of electrochemical reactions should result in a net change in the magnetic susceptibility of species near the electrode.
Magnetic field effects on chemical systems can be broken down into three types: thermodynamic, kinetic, and mass transport. Macroscopic, thermodynamic effects are negligible, although local magnetic field effects may not be. Kinetically, both reaction rates and product distributions can be altered. Transport effects can lead to flux enhancements of several-fold. Quantum mechanical effects are also possible, especially on very short length scales, below 10 nm. The following summarizes what has been done with homogeneous fields applied to solutions and cells with external laboratory magnets.
A magnetic field applied homogeneously by placing a solution between the poles of a laboratory magnet will have a negligible nonexponential effect on the free energy of reaction. xcex94Gm=xe2x88x920.5xcex94XmB2 J/mole, where xcex94Gm is the change of the free energy of reaction due to the magnetic field, xcex94Xm is the difference in magnetic susceptibility of the products and reactants, and B is the magnetic induction in gauss. For the conversion of a diamagnetic species into a paramagnetic species, xcex94Xmxe2x89xa60.01 cm3/mole. In a 1 Telsa (T) (1 Tesla=10 kGauss) applied field, |xcex94Gm|xe2x89xa60.05 J/mole. Even in the strongest laboratory fields of 10 T, the effect is negligible compared to typical free energies of reaction (xcx9ckJ/mole). These are macroscopic arguments for systems where the magnet is placed external to the cell and a uniform field is applied to the solution. Microscopically, it may be possible to argue that local fields in composites are substantial, and molecules in composites within a short distance of the source of the magnetic field experience strong local fields. For example, for a magnetic wire or cylinder, the magnetic field falls off over a distance, x, as xxe2x88x923. The field experienced by a molecule 1 nm from the magnet is roughly 1021 times larger than the field experienced at 1 cm. This argument is crude, but qualitatively illustrates the potential advantage of a microstructural magnetic composite. (As an example, in the magnetic/Nafion (DuPont) composites, a larger fraction of the redox species are probably transported through the 1.5 nm zone at the interface between the Nafion and the magnetic particles.) These redox species must therefore experience large magnetic fields in close proximity to the interface.
Reaction rates, k, are parameterized by a pre-exponential factor, A, and a free energy of activation, xcex94G‡; k=A exp[xe2x88x92xcex94G‡/RT]. An externally applied, homogeneous magnetic field will have little effect on xcex94G‡, but can alter A. Nonadiabatic systems are susceptible to field effects. Magnetic fields alter the rate of free radical singlet-triplet interconversions by lifting the degeneracy of triplet states (affecting xcex94G‡); rates can be altered by a factor of three in simple solvents. Because magnetic coupling occurs through both electronic nuclear hyperfine interactions and spin-orbit interactions, rates can be nonmonotonic functions of the applied field strength. Photochemical and electrochemical luminescent rates can be altered by applied fields. For singlet-triplet interconversions, magnetic fields alter product distributions when they cause the rate of interconversion to be comparable to the rate at which free radicals escape solvent cages. These effects are largest in highly viscous media, such as polymer films and micellar environments. Larger effects should be observed as the dimensionality of the system decreases. For coordination complexes, photochemical and homogeneous electron transfer rates are altered by magnetic fields. Spin-orbit coupling is higher in transition metal complexes than organic radicals because of higher nuclear charge and partially unquenched orbital angular momentum of the d-or f-shell electrons. The rate of homogeneous electron transfer between Co(NH3)63+ and Ru(NH3)62+ is below that expected for diffusion controlled reactions; in a 7 T magnetic field, the rate is suppressed two to three-fold. It has been argued that xcex94Xm (and xcex94Gm) is set by the magnetic susceptibility of the products, reactants, and activated complex, and a highly paramagnetic activated complex accounts for the field effect. For reversible electron transfer at electrodes in magnetic fields, no significant effect is expected. For quasireversible electron transfer with paramagnetic and diamagnetic species, electron transfer rates and transfer coefficients (xcex1) are unchanged by magnetic fields applied parallel to electrodes. Magnetic fields applied perpendicular to electrodes in flow cells generate potential differences, which just superimpose on the applied electrode potentials. Potentials of 0.25V have been reported. Reversing the applied magnetic field reverses the sign of the potential difference. This effect does not change standard rate constants, only the applied potential.
Magnetically driven mass transport effects have been studied in electrochemical cells placed between the poles of large magnets. Effects vary depending on the orientation of the electrode, the relative orientation of the magnetic field and the electrode, forced or natural convection, and the relative concentrations of the redox species and electrolyte. Three cases are illustrated in FIGS. 1, 2 and 3.
For a charged species moving by natural or forced convection parallel to an electrode and perpendicular to a magnetic field which is also parallel to the electrode, a Lorentz force is generated which moves the charged particle toward the electrode (FIG. 1). This magnetohydrodynamic effect is characterized by
F=q(E+vxc3x97B)xe2x80x83xe2x80x83(1)
where F, E, v, and B are vectors representing the Lorentz force on the charged species, the electric field, the velocity of the moving species, and the magnetic field, respectively; and q is the charge on the species. For flow cells and vertical electrodes, flux enhancements of a few-fold and reductions in the overpotential of a few tenths volts have been found in the presence of the magnetic field. Also, embedded in Equation 1 is the Hall effect; when a charged species moves through a perpendicular magnetic field, a potential is generated. This potential superimposes on the applied potential and causes migration in low electrolyte concentrations.
When the electrode and magnetic field are parallel to the earth, thermal motion leads to vortical motion at the electrode surface unless the field (B) and the current density (j) are spatially invariant and mutually perpendicular (see FIG. 2). This is parameterized as:
Fv=cxe2x88x921[jxc3x97B].xe2x80x83xe2x80x83(2)
In Equation (2) Fv is the vector of magnetic force per volume and c is the speed of light. In general, these forces are smaller than Lorentz forces; flux enhancements of a few-fold and potential shifts of 10 to 20 mV are observed. Flux enhancements of paramagnetic and diamagnetic species are similar, but paramagnetic electrolytes enhance the flux of diamagnetic Zn2+ two-fold. Vortices suppress thermal motion and eddy diffusion.
The final configuration, shown in FIG. 3, is for the magnetic field perpendicular to the electrode surface, and, therefore, parallel to the electric field. Various, and sometimes inconsistent, results are reported for several configurations: for vertical electrodes in quiescent solution, flux enhancements of xe2x89xa61000%; for electrodes parallel to the earth with forced convection, flux retardations of 10%; and for electrodes parallel to the earth and no forced convection, both enhancements and no enhancements are reported.
The above summarizes the thermodynamic, kinetic, and mass transport effects for systems where the magnetic field is applied uniformly across a cell with an external magnet. None of these macroscopic effects predict or address properties dependent on the magnetic susceptibility of the redox species. Quantum mechanical effects may also be important, especially on short length scales.
Since the incomplete reduction of oxygen limits the efficiency of H2/O2 solid polymer electrolyte fuel cells, the cathode must be pressurized about five-fold over the anode.
Proton exchange membrane (PEM) fuel cell design is one which employs hydrogen as an anode feed and oxygen in air as a cathode feed. These fuels are decomposed electrolytically (to yield water) at electrodes typically modified with a noble metal catalyst. The hydrogen and oxygen are separated from each other by a proton exchange membrane (such as Nafion) to prevent thermal decomposition of the fuels at the noble metal catalyst. The reactions at the cathode and anode can be summarized as follows:                                                         Cathode                                                          Anode                                                                    Net          ⁢                      xe2x80x83                    ⁢          Reaction                      ⁢                                                        O              2                        +                          4              ⁢                              H                +                                      +                          4              ⁢              e                                =                      2            ⁢                          H              2                        ⁢            O                                                                                  2              ⁢                              H                +                                      +                          2              ⁢              e                                =                      H            2                                                                                  O              2                        +                          2              ⁢                              H                2                                              =                      2            ⁢                          H              2                        ⁢            O                                ⁢                                                                                          E                  cathode                  xc2x0                                =                                  1.23                  ⁢                                      xe2x80x83                                    ⁢                  V                                                                                                                          E                  anode                  xc2x0                                =                                  0.00                  ⁢                                      xe2x80x83                                    ⁢                  V                                                                                                              E            cell            xc2x0                    =                      1.23            ⁢                          xe2x80x83                        ⁢            V                              
However, the fuel cell is typically run under non-equilibrium conditions, and, as such, is subject to kinetic limitations. These limitations are usually associated with the reaction at the cathode.
O2+4H++4e=2H2O Exc2x0cathode=1.23V
As the reaction at the cathode becomes increasingly kinetically limited, the cell voltage drops, and a second reaction path, the two electron/two proton reduction of oxygen to peroxide, becomes increasingly favored. This consumes oxygen in two electron steps with lower thermodynamic potential.
O2+2H++2e=H2O2 Exc2x0H2O2=0.68V
The standard free energy of this reaction is 30% of the free energy available from the four electron reduction of oxygen to water. The decrease in current associated with the decreased number of electrons transferred and the decreased cell potential couple to yield substantially lower fuel cell power output.
One approach to enhance the efficiency of the cathodic reaction is to increase the concentration (pressure) of the feeds to the cathodexe2x80x94protons and oxygenxe2x80x94so as to enhance the flux (i.e., the reaction rate at the cathode in moles/cm2s) at the cathode. The proton flux is readily maintained at a sufficiently high value by the proton exchange membrane (usually Nafion) so as to meet the demand set by the cathode reaction. Normally, the method of enhancing the flux and biasing the reaction to favor the formation of water is to pressurize the air feed to the cathode. Pressures of 5-10 atmospheres are typical.
The need to pressurize air to the cathode in PEM fuel cells has been a major obstacle in the development of a cost effective fuel cell as a replacement for the internal combustion engine, e.g., in a vehicle. In particular, pressurization of the cathode requires compressors. In transportation applications, power from the fuel cell is needed to run the compressor. This results in approximately 15% reduction in the power output of the total fuel cell system.
By developing a passive pressurization method for a fuel cell, the mechanical pumps could be eliminated from the fuel cell system. This has numerous advantages. The weight of a fuel cell would be decreased almost 40% by eliminating mechanical pumps. With the elimination of the parasitic loss of running the pumps, and improving cathode performance, the fuel cells would provide a higher energy and power density. Any potential shift at the electrode surface driven by the magnetic components can be exploited to enhance the voltage output of the fuel cell, and to overcome the poor kinetics of the cathode. Eliminating the pumps also eliminates the only moving parts of the fuel cell, and thereby, the likelihood of fuel cell failure is drastically reduced.
In current fuel cell design, the cathode is pressurized to approximately five times the pressure of the anode. This pressurization constrains the design of the fuel cell to be sufficiently rigid as to support this pressure. In a magnetically based, passive pressurization scheme, the need for the rigid structure is eliminated. This has two major advantages. First, the weight and bulk of the fuel cell is decreased. Second, the fuel cell is now a flexible device. The flexibility can be exploited in various ways, including placing fuel cells into unusual geometries and structures, thereby exploiting space in structures and devices which might otherwise be lost. Also, the flexible nature of the fuel cell allows a single structure to be divided readily into several smaller cells, which can be connected into different parallel and serial configurations to provide variable voltage and current outputs. Such a division is more complicated in the more rigid structures of a pressurized fuel cell because the encasing walls limit access to the fuel cell electrodes.
It is therefore an object of the invention to provide an improved electrode.
Another object of the invention is to provide a coating on an electrode to enhance the flux of magnetic species to the electrode.
Another object of the invention is to provide a separator to separate magnetic species from each other dependent upon magnetic susceptibility.
Another object of the invention is to provide a method for making a coating for an electrode to improve the flux of magnetic species to the electrode.
Another object of the invention is to provide an improved fuel cell.
Another object of the invention is to provide an improved cathode in a fuel cell.
Another object of the invention is to provide an improved battery.
Another object of the invention is to provide an improved membrane sensor.
Another object of the invention is to provide an improved flux switch.
Another object of the invention is to provide an improved fuel cell cathode with passive oxygen pressurization.
Another object of the invention is to provide an improved separator for separating paramagnetic species from diamagnetic species.
Another object of the invention is to provide an improved electrolytic cell.
Another object of the invention is to provide an improved electrolytic cell for an electrolyzable gas.
Another object of the invention is to provide an improved graded density composite for controlling chemical species transport.
Another object of the invention is to provide an improved dual sensor.
One advantage of the invention is that it can enhance the flux of paramagnetic species to an electrode.
Another advantage of the invention is that it can enhance the flux of oxygen to the cathode in a fuel cell, equivalent to passive pressurization.
Another advantage of the invention is that it can separate paramagnetic, diamagnetic, and nonmagnetic chemical species from a mixture.
Another advantage of the invention is that it can separate chemical species according to chemical, viscosity, and magnetic properties.
Another advantage of the invention is that it can take advantage of magnetic field gradients in magnetic composites.
Another advantage of the invention is that it can be designed to work with internal or external magnetic fields, or both.
One feature of the invention is that it includes a magnetically modified electrode.
Another feature of the invention is that it includes magnetic composites made from ion exchange polymers and non-permanent magnet microbeads with magnetic properties which are susceptible to externally applied magnetic fields.
Another feature of the invention is that it includes magnetic composites made from ion exchange polymers and organo-Fe (superparamagnetic or ferrofluid) or other permanent magnetic and nonpermanent magnetic or ferromagnetic or ferrimagnetic material microbeads which exhibit magnetic field gradients.
These and other objects, advantages and features are accomplished by a separator arranged between a first region containing a first type of particle and a second type of particle and a second region, comprising: a first material having a first magnetism; a second material having a second magnetism; a plurality of boundaries providing a path between the first region and the second region, each of the plurality of boundaries having a magnetic gradient within the path, the path having an average width of approximately one nanometer to approximately several micrometers, wherein the first type of particles have a first magnetic susceptibility and the second type of particles have a second magnetic susceptibility, wherein the first and the second magnetic susceptibilities are sufficiently different that the first type of particles pass into the second region while most of the second type of particles remain in the first region.
These and other objects, advantages and features are also accomplished by the provision of a cell, comprising: an electrolyte including a first type of particles; a first electrode arranged in the electrolyte; and a second electrode arranged in the electrolyte wherein the first type of particles transform into a second type of particles once the first type of particles reach the second electrode, the second electrode having a surface with a coating which includes: a first material having a first magnetism; a second material having a second magnetism; a plurality of boundaries providing a path between the electrolyte and the surface of the second electrode, each of the plurality of boundaries having a magnetic gradient within the path, the path having an average width of approximately one nanometer to approximately several micrometers, wherein the first type of particles have a first magnetic susceptibility and the second type of particles have a second magnetic susceptibility, and the first and the second magnetic susceptibilities are different.
These and other objects, advantages and features are also accomplished by the provision of a method of making an electrode with a surface coated with a magnetic composite with a plurality of boundary regions with magnetic gradients having paths to the surface of the electrode, comprising the steps of: mixing a first component which includes a suspension of at least approximately 1 percent by weight of inert polymer coated magnetic microbeads containing between approximately 10 percent and approximately 90 percent magnetizable material having diameters at least 0.5 micrometers in a first solvent with a second component comprising at least approximately 2 percent by weight of an ion exchange polymer in a second solvent to yield a casting mixture or a mixed suspension; applying the casting mixture or mixed suspension to the surface of the electrode, the electrode being arranged in a magnetic field of at least approximately 0.05 Tesla and being oriented approximately 90 degrees with respect to the normal of the electrode surface; and evaporating the first solvent and the second solvent to yield the electrode with a surface coated with the magnetic composite having a plurality of boundary regions with magnetic gradients having paths to the surface of the electrode.
These and other objects, advantages and features are further accomplished by a method of making an electrode with a surface coated with a composite with a plurality of boundary regions with magnetic gradients having paths to the surface of the electrode when an external magnetic field is turned on, comprising the steps of: mixing a first component which includes a suspension of at least 5 percent by weight of inert polymer coated microbeads containing between 10 percent and 90 percent magnetizable nonpermanent magnetic material having diameters at least 0.5 micrometers in a first solvent with a second component comprising at least 5 percent by weight of an ion exchange polymer in a second solvent to yield a casting mixture or a mixed suspension; applying the casting mixture or mixed suspension to the surface of the electrode; evaporating the first solvent and the second solvent to yield the electrode with a surface coated with the composite having a plurality of boundary regions with magnetic gradients having paths to the surface of the electrode when an external magnet is turned on.
These and other objects, advantages and features are also accomplished by an electrode for channeling flux of magnetic species comprising: a conductor; a composite of a first material having a first magnetism and a second material having a second magnetism in surface contact with the conductor, wherein the composite comprises a plurality of boundaries providing pathways between the first material and the second material, wherein the pathways channel the flux of the magnetic species through the pathways to the conductor.
These and other objects, advantages and features are further accomplished by an electrode for effecting electrolysis of magnetic species comprising: a conductor; and magnetic means in surface contact with the conductor for enhancing the flux of the magnetic species in an electrolyte solution to the conductor and thereby effecting electrolysis of the magnetic species.
These and other objects, advantages and features are further accomplished by an electrode for effecting electrolysis of magnetic species comprising: a conductor; and means in surface contact with the conductor for enhancing the flux of the magnetic species to the conductor and thereby effecting electrolysis of the magnetic species.
These and other objects, advantages and features are yet further accomplished by an electrode for electrolysis of magnetic species comprising: a conductor; a composite magnetic material in surface contact with the conductor, the composite magnetic material having a plurality of transport pathways through the composite magnetic material to enhance the passage of the magnetic species to the conductor and thereby effecting electrolysis of the magnetic species.
These and other objects, advantages and features are also accomplished by a system, comprising: a first electrolyte species with a first magnetic susceptibility; a second electrolyte species with a second magnetic susceptibility; and a means for channeling the first electrolyte species with a first magnetic susceptibility preferentially over the second electrolyte species with a second magnetic susceptibility, wherein the means comprises a first material having a first magnetism forming a composite with a second material having a second magnetism.
These and other objects, advantages and features are also accomplished by a system for separating first particles and second particles with different magnetic susceptibilities comprising: a first magnetic material with a first magnetism; and a second magnetic material with a second magnetism working in conjunction with the first magnetic material to produce magnetic gradients, wherein the magnetic gradients separate the first particles from the second particles.
These and other objects, advantages and features are accomplished by a composite material for controlling chemical species transport comprising: an ion exchanger and a graded density layer, wherein the ion exchanger is sorbed into the graded density layer.
These and other objects, advantages and features are further accomplished by a magnetic composite material for controlling magnetic chemical species transport according to magnetic susceptibility comprising: an ion exchanger; a polymer coated magnetic microbead material; and a graded density layer, wherein the ion exchanger and the polymer coated magnetic microbead material are sorbed into the graded density layer.
These and other objects, advantages and features are further accomplished by a composite material for controlling chemical species viscous transport comprising: an ion exchanger; a graded viscosity layer, wherein the ion exchanger is sorbed into the graded viscosity layer.
These and other objects, advantages and features are further accomplished by a magnetic composite material for controlling magnetic chemical species transport and distribution comprising: an ion exchanger; a polymer coated magnetic microbead material; and a graded density layer, wherein the ion exchanger and the polymer coated magnetic microbead material are sorbed into the graded density layer forming a gradient in the density of the polymer coated magnetic microbead material substantially perpendicular to a density gradient in the graded density layer.
These and other objects, advantages and features are further accomplished by a magnetic composite material for controlling magnetic chemical species transport and distribution comprising: an ion exchanger; a polymer coated magnetic microbead material; and a graded density layer, wherein the ion exchanger and the polymer coated magnetic microbead material. are sorbed into the graded density layer forming a gradient in the density of the polymer coated magnetic microbead material substantially parallel to a density gradient in the graded density layer.
These and other objects, advantages and features are also accomplished by an ion exchange composite with graded transport and chemical properties controlling chemical species transport comprising: an ion exchanger; and a staircase-like graded density layer having a first side and a second side, wherein the ion exchanger is one of sorbed into the graded density layer and cocast on the graded density layer and the staircase-like graded density layer and the ion exchanger are contained within the first side and the second side, wherein the first side is in closer proximity to the source of the chemical species and the second side is more distal to the source of the chemical species, and wherein the staircase-like graded density layer has lower density toward the first side and higher density toward the second side, substantially increasing in density in a direction from the first side toward the second side.
These and other objects, advantages and features are also accomplished by an ion exchange composite with graded transport and chemical properties controlling chemical species transport comprising: an ion exchanger; and a staircase-like graded density layer having a first side and a second side, wherein the ion exchanger is one of sorbed into the graded density layer and cocast on the graded density layer, and the ion exchanger and the stair case-like graded density layer are contained within the first side and the second side, wherein the first side is in closer proximity to the source of the chemical species and the second side is more distal to the source of the chemical species, and wherein the staircase-like graded density layer has higher density toward the first side and lower density toward the second side, substantially decreasing in density in a direction from the first side toward the second side.
These and other objects, advantages and features are accomplished also by a dual sensor for distinguishing between a paramagnetic species and a diamagnetic species comprising: a magnetically modified membrane sensor; and an unmodified membrane sensor, wherein the magnetically modified membrane sensor preferentially enhances the concentration of and allows the detection of the paramagnetic species over the diamagnetic species and the unmodified membrane sensor enhances the concentration of and allows the detection of the diamagnetic species and the paramagnetic species, enabling the measurement of the concentration of at least the paramagnetic species.
These and other objects, advantages and features are further accomplished by a dual sensor for distinguishing between a paramagnetic species and a nonmagnetic species comprising: a magnetically modified membrane sensor; an unmodified membrane sensor, wherein the magnetically modified membrane sensor preferentially enhances the concentration of and allows the detection of the paramagnetic species over the nonmagnetic species and the unmodified membrane sensor enhances the concentration of and allows the detection of the nonmagnetic species and the paramagnetic species, enabling the measurement of the concentration of at least the paramagnetic species.
These and other objects, advantages and features are further accomplished by a dual sensor for distinguishing between a first diamagnetic species and a second diamagnetic species comprising: a magnetically modified membrane sensor; and a differently magnetically modified membrane sensor; wherein the magnetically modified membrane sensor preferentially enhances the concentration of and allows the detection of the first diamagnetic species over the second diamagnetic species and the differently magnetically modified membrane sensor enhances the concentration of and allows the detection of the second paramagnetic species and the diamagnetic species, enabling the measurement of the concentration of at least the first diamagnetic species.
These and other objects, advantages and features are further accomplished by a dual sensor for distinguishing between a first paramagnetic species and a second paramagnetic species comprising: a magnetically modified membrane sensor; and a differently magnetically modified membrane sensor, wherein the magnetically modified membrane sensor preferentially enhances the concentration of and allows the detection of the first paramagnetic species over the second paramagnetic species and the differently magnetically modified membrane sensor enhances the concentration of and allows the detection of the second paramagnetic species and the first paramagnetic species, enabling the measurement of the concentration of at least the first paramagnetic species.
These and other objects, advantages and features are further accomplished by a dual sensor for distinguishing between a diamagnetic species and a nonmagnetic species comprising: a magnetically modified membrane sensor; and an unmodified membrane sensor, wherein the magnetically modified membrane sensor preferentially enhances the concentration of and allows the detection of the diamagnetic species over the nonmagnetic species and the unmodified membrane sensor enhances the concentration of and allows the detection of the nonmagnetic species and the diamagnetic species, enabling the measurement of the concentration of at least the diamagnetic species.
These and other objects, advantages and features are further accomplished by a flux switch to regulate the flow of a redox species comprising: an electrode; a coating on the electrode, wherein the coating is formed from a composite comprising: a magnetic microbead material with aligned surface magnetic field; an ion exchange polymer; and an electro-active polymer in which a first redox form is paramagnetic and a second redox form is diamagnetic, wherein the flux switch is actuated by electrolyzing the electro-active polymer from the first redox form ordered in the magnetic field established by the coating to the second redox form disordered in the magnetic field.
These and other objects, advantages and features are also accomplished by a flux switch to regulate the flow of a chemical species comprising: an electrode; and a coating on the electrode, wherein the coating is formed from a composite comprising: a non-permanent magnetic microbead material; an ion exchange polymer; and a polymer with magnetic material contained therein in which a first form is paramagnetic and a second form is diamagnetic, wherein the flux switch is actuated by reversibly converting from the paramagnetic form to the diamagnetic form when an externally applied magnetic field is turned on or off.
The above and other objects, advantages and features of the invention will become more apparent from the following description thereof taken in conjunction with the accompanying drawings.